The present invention relates to a head driving device for driving various portions of a liquid ejecting head.
In a related art, there is proposed a circuit for driving a printing head with an object of enabling to eject ink stably from a nozzle opening even when a number of pressure generating elements (for example, piezoelectric elements) to be driven is varied. The related printing head driving circuit applies a predetermined potential (correcting potential) from a first switching speed correcting circuit and a second switching speed correcting circuit to a base of a transistor at a post stage of transistors connected in Derlington connection in a drive signal outputting circuit via a terminal for applying the correcting potential, thereby, it is possible to execute assisting injection of charge to the base of the transistor at the post stage or assisting flow out of charge from the base. As a result, a switching speed of the transistor of the post stage can arbitrarily be corrected in accordance with the potential applied to the terminal for applying the collecting potential (refer to, for example, JP-A-2000-211126).
Meanwhile, according to a related printing head driving circuit shown in FIG. 7, by making a potential of a drive voltage transmitting line 11 for connecting a power amplifying circuit 3 and an analog switch 7 or the like on a side of a printing head 5 (hereinafter, described as “COM potential”) coincide with a bias potential of a piezoelectric element 9 when printing is stopped, stability of printing is increased and service life of the piezoelectric element 9 is also prolonged. However, an output voltage from a direct current power source of 42V is applied to a side of a drive voltage generating circuit 1 including the power amplifying circuit 3 as a drive power source. Also, charge charged from a direct current power source of 5V to a capacitor 15 via a resistor 13 is applied to the side of the piezoelectric element 9 as the bias voltage of the piezoelectric element 9. Therefore, a potential difference is produced between the COM potential and the bias potential of the piezoelectric element 9. As a result, a leak current is made to flow to the piezoelectric element 9 through the drive voltage transmitting line 11. Therefore, there poses a problem that a power consumption amount of the printer at standby state is considerable.
Further, in the related printing head driving circuit shown in FIG. 7, a capacitance of an (electrolytic) capacitor 15 for applying a bias voltage to respective piezoelectric elements 9 is far larger than a capacitance of a plurality of pieces of the piezoelectric elements 9 (in FIG. 7, only one piece of the piezoelectric element designated by numeral 9 is illustrated for convenience of illustration and explanation) provided at respective nozzles. This is because whereas a piezoelectric element having a small capacitance equal to or smaller than, for example, 1 μF is used for each of the piezoelectric elements 9, an (electrolytic) capacitor having a large capacity of about, for example, 4000 μF is used for the (electrolytic) capacitor 15.
The reason of using the (electrolytic) capacitor having the capacitance far larger than the capacitance of the piezoelectric elements 9 in this way as the capacitor 15 is that a voltage charged to the capacitor 15 through a resistor 13 (of, for example, 400μΩ) from a direct current power source (of, for example, 5V) is applied from the capacitor 15 to the respective piezoelectric elements 9 as the bias voltage. In other words, since the capacitor 15 achieves a function as a storage battery, the capacitor having the large capacitance needs to use as the capacitor 15. Therefore, a time constant (CR) determined by a product of the capacitance (4000 μF) of the capacitor 15 by a resistance value (4000μΩ) of the resistor 13 is large and therefore, time is taken for charging the capacitor 15 until an output voltage from the capacitor 15 reaches the above-described power source voltage (for example, 5V) (for example, about several second are required).
The printing head driving circuit illustrated in FIG. 7 does not pose a serious problem even when time is taken in charging the above-described capacitor 15 from the above described direct current power source, in the case in which the drive power source is temporarily made OFF to stop printing operation of the printer and thereafter, the drive power source is made ON again to restart the printing operation of the printer. Because normally, the printer needs a time period to some degree until the printing operation can be carried out since the drive power source has been switched on. However, there is a case in which the printer is intended to be brought into a standby state (awaiting state) by temporarily stopping to charge the capacitor 15 from the direct current power source of 5V for saving power or the like. In that case, when time is taken in charging the capacitor 15 as described above, there poses a problem that time is taken for recovering the printer from the standby state to a state of capable of carrying out printing operation.